1. Field of the Invention
The present invention relates generally to mushroom cultivation, and more particularly to an improved nutrient supplement for promoting mushroom growth.
2. Description of the Prior Art
(A) Commercial Growing Practices
Commercial mushroom cultivation is essentially a four-phase operation employing the following steps:
(1) composting - forming a nutrient substrate (compost bed) upon which mushrooms can be grown;
(2) spawning - impregnating the compost bed with mushroom mycelia;
(3) casing - after the mycelia have suitably developed, covering the mycelia-permeated compost bed with a layer of soil, peat, or sand; and
(4) harvesting or "cropping" the developed mushrooms. The mushroom growth process exhausts the necessary nutrients from the compost bed. As a result, after the mushroom crop has been harvested, the nutrient-depleted compost bed is discarded and the cultivation operation is repeated.
Commercial mushroom facilities utilize composted organic materials prepared from a mixture of cereal straws, organic fertilizers, and other nutrients. The action of microorganisms on the straw/fertilizer/nutrient mixture results in a substrate which is selective for the colonization of mushrooms without undo competition from other fungi or microorganisms. In addition to providing a substrate upon which mushrooms can be grown, the compost serves as a source of nutrients essential for mushroom growth.
The prepared compost is preferably pasteurized in order to deactivate any residual microorganisms and then is impregnated with mushroom inocula (mycelia) in a step referred to as "spawning". Thereafter, the mycelium-impregnated compost is maintained at controlled conditions for a period of two to three weeks until the hyphae of the mycelium have permeated the compost.
The next stage of commercial mushroom production, referred to as "casing", involves covering the mycelia-permeated (colonized) compost with a thin layer of peat (preferably buffered with calcium carbonate), soil or sand. This allows the mushrooms to fruit or "flush".
The first flush of mushrooms generally occurs approximately three weeks after casing. After harvesting this first flush (or "break"), the commercial bed will produce two to four additional flushes or breaks until the compost becomes sufficiently depleted of essential nutrients so a to become uneconomical. The compost is then discarded.
(B) Use of Growth-Enhancing Supplements
Enhanced mushroom yields can be obtained by adding supplementary nutrients either to the compost bed (after completion of the composting step) or to the mycelia-impregnated compost up to the time of casing. Addition of nutrients after casing is generally no beneficial.
Most commercially-employed nutrient supplements are proteinaceous in nature; both animal and vegetable-derived materials have been utilized. Although these protein supplements are relatively expensive, they have been shown to produce sufficiently enhanced yields to be economically attractive. Up until now, the presence of larger amounts of carbohydrates in supplements has been perceived as being detrimental to mushroom yields.
The addition of available supplementary nutrients can result in adverse effects to the mushroom crop. In addition to fostering mushroom growth, directly utilizable nutrients can be metabolized by competing, faster-growing microorganisms present in the compost bed. Consumption of nutrients by competing organisms has two deleterious effects: not only is the expensive nutrient removed from its intended use as a mushroom growth supplement, but the intense microbial activity also acts to raise the temperature of the mushroom bed. High temperatures have adverse effects on mushroom mycelia, and can destroy the growing mushroom crop.
Another difficulty with the use of directly utilizable supplements is that enhanced yields are observed only in the first flush. That is, by the advent of the subsequent flushes, the added nutrient supply has been reduced or even exhausted and little yield stimulation is observed.
One approach to dealing with the problem resulting from nutrient-rich systems is to retard the rate of release of the nutrient from the supplement. In Carroll, et al. U.S. Pat. No. 3,942,969, this retardation is accomplished by denaturing a protein-containing supplement with heat or chemicals prior to adding the nutrient supplement to the compost bed. Denatured protein is reported to greatly lessen the availability of the nutrient to competing microorganisms while maintaining its availability to the growing mushrooms. The patent also teaches that the presence of carbohydrates in the supplements is objectionable, but that such materials can be tolerated in small amounts. The gains in mushroom yields resulting from the process described in the foregoing patent are at least partially offset by the economic costs involved in the denaturing step.
Another approach to the problem resulting from the use of directly-utilizable nutrient supplements is illustrated in Wu, et al. U.S. Pat. No. 4,534,781, which utilizes a hydrophobic material (e.g., paraffin wax or shellac) to coat a protein-containing nutrient supplement. The patent teaches that such a coating will resist attack by competing organisms and will delay the availability of the nutrient to the mushroom mycelia until the coating is gradually removed during the mushroom growth period. The patent teaches that one advantage of the hydrophobic coating is the lessening of hydration of the nutrient supplement. Since most molds require moisture for growth, the presence of such a hydrophobic coating eliminates an essential requirement for rapid growth of such competing microorganisms.